/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.streaming.api.operators.sorted.state;

import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.runtime.state.internal.InternalMergingState;

import java.util.Collection;

/**
 * An abstract class with a common implementation of {@link InternalMergingState#mergeNamespaces(Object, Collection)}.
 */
abstract class MergingAbstractBatchExecutionKeyState<K, N, V, IN, OUT>
		extends AbstractBatchExecutionKeyState<K, N, V>
		implements InternalMergingState<K, N, IN, V, OUT> {
	protected MergingAbstractBatchExecutionKeyState(
			V defaultValue,
			TypeSerializer<K> keySerializer,
			TypeSerializer<N> namespaceSerializer,
			TypeSerializer<V> stateTypeSerializer) {
		super(defaultValue, keySerializer, namespaceSerializer, stateTypeSerializer);
	}

	protected abstract V merge(V target, V source) throws Exception;

	@Override
	public void mergeNamespaces(N target, Collection<N> sources) throws Exception {
		if (sources == null || sources.isEmpty()) {
			return;
		}

		setCurrentNamespace(target);
		V targetValue = getCurrentNamespaceValue();
		for (N source : sources) {
			setCurrentNamespace(source);
			V sourceValue = getCurrentNamespaceValue();
			if (targetValue == null) {
				targetValue = sourceValue;
			} else if (sourceValue != null) {
				targetValue = merge(targetValue, sourceValue);
				clear();
			}
		}
		setCurrentNamespace(target);
		setCurrentNamespaceValue(targetValue);
	}

	@Override
	public V getInternal() {
		return getCurrentNamespaceValue();
	}

	@Override
	public void updateInternal(V valueToStore) {
		setCurrentNamespaceValue(valueToStore);
	}
}
